While there were no casualties, all the patients had to be evacuated, Rajab said by telephone.

A worker with the Syrian American Medical Society (SAMS) reported a similar attack. NBC News was not able to independently confirm the separate accounts but they appeared consistent.

Russian-made cluster bombs — weapons that kill indiscriminately and inflict long-lasting damage — were used in an attack on the same hospital earlier this week, a video obtained by NBC News appeared to show.